Because my camera gets rented out to be used with large cinema zooms with real marks that are used with a manual follow focus. This requires a proper rod setup.
I love your mounts Jacek ( I have owned 2 of them ) but some people just don't want to use stills zooms no matter how hard you try to promote it. It's nice to be able to have a lightweight configuration but most of the time these cameras have monitors, matte boxes, follow focus', cinetape etc attached to them. For that we need a rod and usually a top plate system.
I had a rental company for about 10 years - I get it. I shed some blood, sweat, and tears during that time. We have focused our designs on the top of the camera so that you can make better choices for what you do with the bottom. Everyone has different needs, hopes, and desires. MANY shoots never leave a hard support like tripod or dolly. MANY shoots never see a tripod. The best shoulder solution (in my slightly humble opinion) is one that is very flexible. One that allows a fast and easy transition from a properly supported 24-290 to a well balanced handheld config with a small prime. I learned a long time ago, that making those decisions based on what is right instead of what is cheapest pays off. It can sting a little if you are paying more than you hoped for, but divided by the life of the camera - the best accessories are usually the cheapest option. Lower frustration, quicker setups, one extra shot per day. I know this thread is about the "best" shoulder solution so I should not get too far off topic.
Here is a pic of our F55 kit which can go from Doc mode to big Hollywood feature configuration very quickly with camera controlled power distro, audio, etc without getting in the way of how you mount it - shoulder or tripod. To best contribute to making the "best" shoulder system - we let everyone else duke it out while we complete the system with all the other pieces you need to have a slick shoulder setup. It allows the EVF to be positioned anywhere on the camera with very little effort so you can go from handheld to studio quick and easy - no tools.
This pic has a Micron on the bottom that makes quick work of going from 19mm heavy to 15mm LWS. Flexibility.

